Method for preventing or reducing contamination of an immersion type projection apparatus and an immersion type lithographic apparatus

ABSTRACT

A method for preventing or reducing contamination of an immersion type projection apparatus is disclosed. The apparatus includes at least one immersion space that is at least partially filled with a liquid when the apparatus projects a beam of radiation onto a substrate. The method includes rinsing at least part of the immersion space with a rinsing liquid before the apparatus is used to project the beam of radiation onto a substrate.

FIELD

The present invention relates to a method for preventing or reducingcontamination of an immersion type projection apparatus. The presentinvention also relates to an immersion type lithographic apparatus.

BACKGROUND

A known projection apparatus is a lithographic apparatus. A lithographicapparatus is a machine that applies a desired pattern onto a substrate,usually onto a target portion of the substrate. A lithographic apparatuscan be used, for example, in the manufacture of integrated circuits(ICs). In that instance, a patterning device, which is alternativelyreferred to as a mask or a reticle, may be used to generate a circuitpattern to be formed on an individual layer of the IC. This pattern canbe transferred onto a target portion (e.g. comprising part of one, one,or several dies) on a substrate (e.g. a silicon wafer). Transfer of thepattern is typically via imaging onto a layer of radiation-sensitivematerial (resist) provided on the substrate. In general, a singlesubstrate will contain a network of adjacent target portions that aresuccessively patterned. Known lithographic apparatus include so-calledsteppers, in which each target portion is irradiated by exposing anentire pattern onto the target portion at one time, and so-calledscanners, in which each target portion is irradiated by scanning thepattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to utilize immersion lithography, for example usingan immersion type lithographic apparatus. As an example, it has beenproposed to immerse the substrate in a lithographic projection apparatusin an immersion liquid having a relatively high refractive index, e.g.water, so as to fill the space between the final optical element of theprojection lens and the substrate. The point of this is to enableimaging of smaller features because the exposure radiation will have ashorter wavelength in the liquid than in air or in a vacuum. (The effectof the liquid may also be regarded as increasing the effective NA of thesystem).

Submersing the substrate or substrate and substrate table in a bath ofliquid (see for example U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that must be accelerated during a scanningexposure. This may require additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

It has also been proposed to apply a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal optical element of the projection system and the substrate (thesubstrate generally has a larger surface area than the final opticalelement of the projection system). Ways which have been proposed toarrange for this are disclosed, for example, in WO 99/49504 and EP 1 429188 A2.

SUMMARY

It is desirable to prevent or reduce contamination in an immersion typeprojection apparatus.

According to an embodiment of the invention, there is provided a methodfor preventing or reducing contamination of an immersion type projectionapparatus. The apparatus includes at least one immersion space that isat least partially filled with a liquid when the apparatus projects abeam of radiation onto a substrate. The method includes rinsing at leastpart of the immersion space with a rinsing liquid before the apparatusis used to project the beam of radiation onto a substrate.

According to another embodiment, there is provided a method forpreventing or reducing contamination of a lithographic projectionapparatus. The apparatus includes a substrate holder constructed to holda substrate, a patterning device holder constructed to hold a patterningdevice, a projection system, and an immersion system configured to atleast partially fill an immersion space of the apparatus with a liquid.The method includes moving at least one of the immersion system and atleast part of the apparatus relative to each other, and rinsing the atleast part of the apparatus with the liquid before the apparatus is usedto project a patterned beam of radiation onto a target portion of asubstrate.

According to another embodiment, there is provided a method forpreventing or reducing contamination of a lithographic projectionapparatus. The apparatus includes an immersion space. The methodincludes filling at least part of the immersion space with a rinsingliquid for at least one minute.

According to an embodiment, there is provided a method for preventing orreducing contamination of a lithographic projection apparatus. Theapparatus includes a substrate holder constructed to hold a substrate, apatterning device holder constructed to hold a patterning device, aprojection system, and an immersion space. The method includes fillingat least part of the immersion space with a rinsing liquid during anidle time of the apparatus to prevent or reduce substrate contaminationduring at least one subsequent start-up run of the apparatus.

According to an embodiment, there is provided an immersion typelithographic apparatus that includes at least one immersion space, andan immersion system configured to at least partially fill the immersionspace with a liquid. The apparatus is configured to rinse at least partof the immersion space with a rinsing liquid before the apparatus isused to project a patterned beam of radiation onto a substrate.

According to an embodiment, there is provided an immersion typelithographic apparatus that includes at least one storage space orcompartment to store at least one dummy substrate or substrate shapedobject in-situ.

According to an embodiment, there is provided an immersion typelithographic apparatus that includes at least one storage space orcompartment to store at least one dummy patterning device or patterningdevice shaped object in-situ.

According to an embodiment, there is provided a computer programcontaining one or more sequences of machine-readable instructionsconfigured to carry out a method for preventing or reducingcontamination of an immersion type projection apparatus when thecomputer program is being executed by a computer. The apparatus includesat least one immersion space that is at least partially filled with aliquid when the apparatus projects a beam of radiation onto a substrate.The method includes rinsing at least part of the immersion space with arinsing liquid before the apparatus is used to project the beam ofradiation onto a substrate.

According to an embodiment, there is provided a method for preventing orreducing contamination of a lithographic projection apparatus. Theapparatus includes a space that is to be provided with a liquid throughwhich a beam of radiation can be transmitted. The method includesoperating the lithographic apparatus, and subsequently rinsing at leastpart of the space with a rinsing liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 schematically depicts a detail of the embodiment of FIG. 1;

FIG. 3 schematically depicts a top view of a substrate and a substratesupport of the embodiment of FIG. 1, showing different immersion spacelocations;

FIG. 4 shows a detail of an alternative embodiment; and

FIG. 5 shows results, concerning particle counts of different test runs.

DETAILED DESCRIPTION

In the present application, the same or similar features are generallydenoted by the same or similar reference signs.

FIG. 1 schematically depicts a projection apparatus 1 according to oneembodiment of the invention.

According to an embodiment of the invention, the apparatus 1 is alithographic apparatus, and is arranged to project a pattern from apatterning device MA onto a substrate W.

The apparatus can comprise: an illumination system (illuminator) ILconfigured to condition a radiation beam B (e.g. UV radiation or another type of radiation); a support structure (e.g. a mask table) MTconstructed to support a patterning device (e.g. a mask) MA andconnected to a first positioner PM configured to accurately position thepatterning device in accordance with certain parameters; a substratetable (e.g. a wafer table) WT constructed to hold a substrate (e.g. aresist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters; and a projection system (e.g. a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g. comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” as used herein should be broadlyinterpreted as referring to any device that can be used to impart aradiation beam with a pattern in its cross-section such as to create apattern in a target portion of the substrate. It should be noted thatthe pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for exampleif the pattern includes phase-shifting features or so called assistfeatures. Generally, the pattern imparted to the radiation beam willcorrespond to a particular functional layer in a device being created inthe target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” as used herein should be broadlyinterpreted as encompassing any type of projection system, includingrefractive, reflective, catadioptric, magnetic, electromagnetic andelectrostatic optical systems, or any combination thereof, asappropriate for the exposure radiation being used, or for other factorssuch as the use of an immersion liquid or the use of a vacuum. Any useof the term “projection lens” herein may be considered as synonymouswith the more general term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam B, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PS. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In an embodiment of the present invention, the projection apparatus 1 isof a type wherein at least a portion of the substrate is covered by aliquid having a relatively high refractive index, e.g. water or an othersuitable liquid, so as to fill an immersion space 10 between theprojection system and the substrate (see FIG. 2). An immersion liquidmay also be applied to other spaces 10′ in the lithographic apparatus 1,for example, between the mask MA and the projection system PS (see FIG.4). Immersion techniques as such are well known in the art forincreasing the numerical aperture of projection systems. The term“immersion” as used herein does not mean that a structure, such as asubstrate, must be submerged in liquid, but generally only means thatliquid is located between the projection system on one side and thesubstrate and/or mask MA on an opposite side during exposure. Forexample, the apparatus can have a similar construction as the apparatusdescribed in EP 1 429 188 A2, which has been incorporated in the presentapplication by reference in its entirety, or a different construction.

FIG. 2 shows a detail of the apparatus of FIG. 1. FIG. 2 depicts animmersion space 10 which abuts at least part of a projection system PS.Particularly, in FIG. 2, the immersion space 10 extends between a finaloptical element PL of the projection system PS and a substrate W orsubstrate shaped object W, which is positioned on a substrate table WT.The apparatus 1 includes an immersion system, comprising inlet/outletducts 13. During use, the immersion system fills the immersion space 10with a liquid 11 having a relatively high refractive index, e.g. water,via inlet/outlet ducts 13. The liquid has the effect that the radiationof the projection beam has a shorter wavelength in the liquid than inair or in a vacuum, allowing smaller features to be resolved. It is wellknown that the resolution limit of a projection system is determined,inter alia, by the wavelength of the projection beam and the numericalaperture of the system. The presence of the liquid may also be regardedas increasing the effective numerical aperture. Furthermore, at fixednumerical aperture, the liquid is effective to increase the depth offield.

The configuration of the apparatus can be such that a substantiallycontactless seal is formed to the substrate W around the image field ofthe final optical element PL so that the liquid is confined to fill thespace between the substrate's primary surface, which faces theprojection system PS, and the final optical element PL of the projectionsystem PS. A reservoir, providing the immersion space 10, can be formedby a seal member 12, for example an ‘immersion hood’, positioned belowand surrounding the final optical element PL of the projection systemPS. Thus, the immersion system can be arranged to provide immersionliquid on only a localized area of the substrate W. The seal member 12can form part of the liquid supply system for filling the space betweenthe final optical element PL of the projection system PS and thesubstrate W with a liquid. This liquid is brought into the space belowthe final optical element PL and within the seal member 12. The sealmember 12 preferably extends a little above the final optical element PLof the projection system PS and the liquid rises above the final opticalelement PL so that a buffer of liquid is provided. The seal member 12can have an inner periphery that at the upper end closely conforms tothe shape of the projection system PS or the final optical element PLthereof and may, e.g. be round. At the bottom the inner peripheryclosely conforms to the shape of the image field, e.g. rectangular,though this is not necessarily so. The seal member 12 can besubstantially stationary in the XY plane relative to the projectionsystem PS though there may be some relative movement in the Z direction(in the direction of the optical axis). A seal can be formed between theseal member 12 and the surface of the substrate W, to confine immersionliquid 11 in the immersion space 10. This seal is preferably acontactless seal and may be a gas seal (not shown).

Also, the substrate table WT can be provided with a cover plate or edgeseal member 17. Such an edge seal member 17 can have an upper (asillustrated) primary surface substantially co-planar with the upperprimary surface of substrate W and is closely adjacent to the edge ofthe substrate W so that there is no sudden loss of liquid as the edge ofthe substrate moves under the final optical element PL. Some liquid lossinto the gap may still occur.

Of course there are arrangements in which the whole constructionillustrated in FIG. 2 is positioned upside down so that it is the lowersurfaces of the edge seal member and the substrate which face theprojection system and which are substantially co-planar. The surfacesare therefore be referred to as the primary surfaces which face theprojection system PS rather than upper surfaces. References herein toupper surfaces and lower surfaces may be also appropriately consideredas references to lower and upper surfaces respectively in an upside-downconfiguration.

With such an apparatus, a liquid supply system (e.g. immersion space 10)can be positioned over the edge of the substrate W and can even be movedcompletely off the substrate W. This enables edge portions of thesubstrate W to be imaged during a device manufacturing method, carriedout by the apparatus.

The edge seal member 17 can be provided in various ways, and may, forexample, form an integral part of the substrate table WT or may betemporarily mounted relative to the remainder of the substrate table bythe use of, for example, vacuum suction or through use ofelectromagnetic forces. Also, the edge seal member 17 may be formed ofseveral individual segments, each of which surrounds a portion of theedge of the substrate W.

According to an embodiment, the projection apparatus comprises at leastone said immersion space 10 and a respective immersion system which isconfigured to at least partially fill the immersion space 10 with animmersion liquid 11. The apparatus can be configured to rinse at leastpart of the immersion space 10 with a rinsing liquid 11 before theapparatus is used to project the patterned beam of radiation onto asubstrate W. For example, in an embodiment, the apparatus is beingconfigured to rinse at least part of the immersion space during arelatively long idle operational mode of the apparatus. The apparatuscan be configured to rinse the immersion space substantiallycontinuously until the apparatus projects a patterned radiation beamonto a substrate.

It is advantageous when the apparatus is configured to rinse theimmersion space with said immersion liquid 11. Then, the immersionliquid and rinsing liquid are simply the same liquid 11, so that theapparatus does not have to be provided with a special cleaning device tosupply a particular cleaning liquid to the immersion space.

In an embodiment, the apparatus can be configured to provide an objectin said immersion space 10 and/or in an adjoining position with respectto the immersion space 10 during the rinsing of that space 10, and toremove said object before the apparatus is used to project a patternedradiation beam onto a target portion of a substrate. Said object caninclude, for example, a virgin (non-coated) wafer, a dummy wafer or awafer shaped object. For example, as is shown in FIG. 1, the apparatuscan include at least one storage space or compartment 22, H to storesaid object when the apparatus is used to project a patterned radiationbeam onto a target portion of a normal (resist coated) substrate. Saidstorage space or compartment 22, H can be provided at various differentlocations of or near the apparatus. For example, such a storage space orcompartment can be located in or near the substrate stage 2 of theapparatus, as has been schematically depicted by box 22 in FIG. 1. Sucha storage space or compartment can be arranged in various ways, and caninclude a closable container, a substrate storage box, a substrate robotgripper or any other suitable substrate holder or substrate storingmeans. Such a storage space or compartment is preferably located withinthe apparatus 1, for example near said immersion system (in substratehandler is described in the following).

Alternatively, said storage space or compartment can include or be partof a substrate handler H, which is located outside the substrate stage 2of the apparatus 1. Such a substrate handler H as such is known to theskilled person. Usually, such a substrate handler H can be configured toreceive one or more substrates from an environment of the apparatus 1,to temporarily store the one or more substrates and to transfer the oneor more substrates to the substrate support WT, to be subsequentlyilluminated by the projection system PS. In the present embodiment, forexample, the substrate handler H can be configured to hold or store oneor more substrates, dummy substrates and/or substrate shaped objectsduring a desired period of time, before such a substrate, dummysubstrate and/or substrate shaped object is located on a respectivesubstrate table WT during a rinsing process, for example during an idleoperational period of the apparatus 1.

Besides, the apparatus 1 can include a mechanism (not specificallyshown) which is arranged or configured to transfer substrates W fromsuch a storage space or compartment 22, H to a substrate holder WT, andvice-versa. Such a mechanism is known to the skilled person. Forexample, the substrate handler H and substrate support WT can bearranged or configured in various ways to transfer substratestherebetween. For example, one or more robot arms, conveyors, transportmeans or other transfer mechanisms can be provided to move substrates,dummy substrates or substrate shaped objects from and to desiredsubstrate positions.

Further, the apparatus can include at least one ultra violet radiationsource to illuminate the immersion space 10 with ultraviolet radiationduring the rinsing of that space, before the apparatus is actually usedto transfer a patterned radiation beam onto a normal (resist coated)substrate. For example, the above-mentioned radiation source SO may bearranged and configured to be such an ultra violet radiation source. Onthe other hand, one or more different radiation sources can be providedto illuminate the immersion space 10 with ultraviolet radiation duringthe rinsing.

In the embodiment shown in the FIGS. 1 and 2, said immersion space 10can extend between at least part of a substrate, a dummy substrate, asubstrate-shaped object W and/or substrate table or holder WT, 17 on oneside and a projection system PS on an opposite side during use. Saiddummy substrate can be, for example, a bare silicon wafer, which has notbeen provided with a resist coating layer. For example, as has beenmentioned above, the apparatus can be configured to place a dummysubstrate or a substrate-shaped object on said substrate holder WT, andto subsequently rinse the respective immersion space 10. Also, theapparatus can be configured to have the immersion space 10 at leastreach or include an outer contour of a substrate, dummy substrate orsubstrate-shaped object W, being held by said substrate holder WT,during the rinsing. This is shown in FIG. 3. For example, the apparatuscan be configured to rinse at least an area of the substrate support WT(using said rinsing liquid), which area extends along and/or around anedge of a substrate, dummy substrate or substrate-shaped object, beingheld by the substrate holder WT. In that case, relatively low particleper substrate counts can be obtained when the apparatus is usedsubsequently to illuminate normal substrates as part of a lithographyprocess. For example, the apparatus can be configured to rinse at leastpart of a surface of the substrate holder WT and/or at least part of asurface of the substrate edge seal member 17 of the substrate holder WT,using said immersion space 10 and said rinsing liquid.

Besides, in an embodiment, the apparatus can be configured to move saidsubstrate holder WT with respect to said projection system PS during therinsing or cleaning process, such that the position of the immersionspace 10 changes with respect to the substrate holder during therinsing. This is shown in FIGS. 2 and 3 by arrows Q and R. In FIG. 2,the arrow Q indicated a lateral movement of the substrate holder WT withrespect to the projection system PS and immersion space 10.

In FIG. 3, the arrow R indicates the scanning of the immersion space 10along an edge of the substrate or substrate shaped object W,circumferentially with respect to the substrate or substrate shapedobject W, from a first position 10 ₁ of the immersion space 10 to asecond position 10 ₂. In this way, the inner part of the surface of thesubstrate holder WT, or of the respective substrate edge seal member 17,that extends near a substrate W during a lithography use of theapparatus, can be rinsed with rinsing liquid. Also, in this way,contamination can be removed from an edge slit E extending between thesubstrate or substrate shaped object W on one side and the substrateholder, or optional edge seal member 17, on an opposite side relativelywell.

Besides, the surface of the substrate holder WT surrounding thesubstrate W during use can include other components 21, such as sensors,positioning devices, mirror elements and/or other components, as hasbeen schematically depicted in FIG. 3. In an embodiment of theinvention, the scanning of the immersion space is such, that thosecomponents 21 can also be reached by the immersion system, to rinse theouter surfaces of these components 21.

Movement of the substrate holder WT to scan the immersion space 10 withrespect to the substrate holder WT can be carried out in variousdirections, for example in the directions Q, R as shown in FIGS. 2 and 3and/or in various other scanning directions, as will be clear to theskilled person.

In an embodiment of the invention, the apparatus is configured to startsaid rinsing automatically after a predetermined amount of idle time ofthe apparatus. Also, the apparatus can be configured to start saidrinsing automatically after a predetermined number of lithographicsubstrate exposures (when a patterned radiation beam is being projectedonto the substrates). Moreover, in an embodiment, the apparatus can beconfigured to determine or estimate whether at least part of saidapparatus has reached a certain threshold amount of contamination, andto rinse said apparatus part when it has been determined or estimatedthat that apparatus part has reached the threshold amount ofcontamination. Besides, as has been shown schematically in FIG. 1, theapparatus can comprise a computer control CC to control the apparatus,or to at least control said rinsing. Such a computer control CC can beconfigured, for example, to control the timing of the starting of therinsing process, to count numbers of substrate exposures in order tostart the rinsing process and/or to estimate or determine when a certainapparatus part has reached said threshold amount of contamination. Thecomputer control can be provided by suitable computer software. Forexample, an embodiment of the invention provides a computer programcontaining one or more sequences of machine-readable instructions whichare configured to carry out a method as disclosed in this patentapplication, when the computer program is being executed by a computer.

In an alternative embodiment, schematically depicted in FIG. 4, theimmersion space 10′ can extend at least between a patterning device MAand/or patterning device holder MT on one side and the projection systemon an opposite side. In that case, for example, the apparatus can beconfigured to place a dummy patterning device or a patterning deviceshaped object on said patterning device holder, and to subsequentlyrinse the respective immersion space. It will be clear that theapparatus can also include an immersion space at the wafer stage and animmersion stage at the patterning device stage, for example by combiningthe embodiments of FIGS. 2 and 4.

Also, in an embodiment, the apparatus can include at least two substrateholders WT. Then, the apparatus can be configured to move each substrateholder WT at least to a first position, wherein said immersion spaceextends between at least part of the substrate holder WT on one side andthe projection system PS on an opposite side, and to a respective secondposition, away from said projection system PS. Said second position canbe, for example, near said substrate handler H, to transfer substratesbetween the respective substrate holder and the substrate handler H (seeFIG. 1). According to a further embodiment, the apparatus can beconfigured to subsequently move said various substrate holders WT tosaid first position, to be at least partially rinsed in or near thatposition by said rinsing liquid. Alternatively, the apparatus cancomprise one or more cleaning devices which are configured to at leastpartially clean a substrate holder when that substrate holder is in saidsecond position. Such a cleaning device 20 is schematically depicted inFIG. 1, and may be arranged, for example to rinse a substrate holderwith rinsing fluid when the substrate holder is in or near said secondposition. Such a cleaning device 20 can function similarly to saidimmersion system, by creating and applying a respective immersion space,or in a different way. Besides, such a cleaning device 20 might bearranged to immerse a respective substrate holder completely in asuitable cleaning liquid.

Besides, the apparatus can be configured to determine which of saidvarious substrate holders is most likely to be contaminated and is to berinsed or cleaned first, wherein the apparatus is configured to rinse orclean that substrate holder first which is found to be most likely to becontaminated.

During use, the immersion type projection apparatus shown in FIGS. 1-3can carry out a method for preventing or reducing contamination. To thataim, at least part of the immersion space 10 is being rinsed with arinsing liquid, preferably being said immersion liquid, before theapparatus is used to project the patterned beam of radiation onto aresist coated substrate. As follows from the above, the immersion space10 can simply be rinsed substantially continuously during an idleoperational mode of the apparatus, until the apparatus is used to carryout a lithography process to transfer a patterned radiation beam onto atarget portion of a substrate. Optionally, at least part of theimmersion space and/or the rinsing liquid is being illuminated byultraviolet radiation, for example to disable or kill bacteria. In oneembodiment, the immersion liquid can be transformed into an ultrasoniccleaning bath. In an other embodiment, the immersion liquid is nottransformed into an ultrasonic cleaning bath, i.e. an embodiment whereinthe apparatus 1 does not include an ultrasonic transmitter configured toturn immersion liquid into an ultrasonic cleaning liquid.

Said idle operational mode of the apparatus 1 can include various idletimes. For example, the apparatus can be idle in a device manufacturingplant due to various circumstances, such as the instantaneous substratethroughput of the plant, a temporary halt in the supply of substrates tothe apparatus 1, a downtime of the plant, a certain maintenance periodof the apparatus and/or a different period.

As is shown in FIGS. 2 and 3, a dummy substrate or a substrate-shapedobject W can be provided on said substrate holder WT when the immersionspace is being rinsed with said rinsing liquid, for example to rinse atleast part of the substrate holder WT. For example, during use, beforestaring the rinsing, said dummy substrate or substrate shaped object Wcan be transferred from the in-situ compartment 22, or alternativelyfrom the substrate handler H, to the substrate holder WT.

Also, the substrate holder WT can be provided with said edge seal member17. In that case, an upper surface, or part thereof, of the edge sealmember 17 of the substrate holder WT can be rinsed by the immersionsystem.

After such rinsing, the dummy substrate or the substrate-shaped objectcan be replaced by a true substrate which is to be illuminated by theprojection system PS in a lithography manufacturing method. For example,the dummy substrate or substrate shaped object W can be stored in asuitable storage compartment, for example said in-situ compartment 22 orsaid substrate handler H, during said lithography manufacturing method.After the lithography manufacturing method, for example, when theapparatus is being put into a relatively long idle operational mode, thedummy substrate or substrate shaped object can again be placed onto thesubstrate holder WT, and the substantially continuous rinsing can berepeated.

Also, the location of the immersion space 10 can be being varied duringthe rinsing treatment. For example, the apparatus can move the substrateholder WT with respect to the immersion system and/or projection systemPS, such that the immersion space 10 can subsequently reach differentlocations of the substrate holder (and/or substrate edge seal 17 orother components 21), to remove contamination therefrom. In this way, atleast part of the apparatus can be washed or rinsed by the immersionsystem, preferably simply using the immersion liquid which is also usedduring lithography use of the apparatus. As follows from the above, inan embodiment, the immersion system can wash or rinse at least one slitor aperture E extending in or near the substrate holder WT, particularlysaid edge slit E extending between the substrate or substrate shapedobject W on one side and the substrate holder, or optional edge sealmember 17, on an opposite side relatively well.

In an embodiment, the immersion space is at least partially being filledor flushed with a rinsing liquid, preferably said immersion liquid, forexample for at least one minute, at least one hour, or a different timeperiod. For example, the immersion space 10 can at least partially befilled or flushed with a rinsing liquid substantially continuously forat least one day, including at least one idle operational period or partthereof. Also, different rinsing periods can be utilized, if desired.Also, the immersion space 10 can be at least partially being filled orflushed with a rinsing liquid during an idle time of the apparatus, toprevent or reduce substrate contamination during at least one subsequentstart-up run of the apparatus. Besides, the method can includecirculating an immersion liquid through an immersion space of theapparatus. To provide a substantially contamination free immersionliquid, the immersion liquid can be filtered and/or treated in asuitable manner, as will be clear to the skilled person.

When the apparatus includes at least two substrate holders WT, see forexample European Patent Application No. 03257072.3, the substrateholders WT might be moved subsequently to said first position, to becleaned by the immersion system. Alternatively, one or more of thosesubstrate holders might be cleaned by said optional cleaning device 20,when that substrate holder is in said second position. Also, during idletime, one or more of the substrate holders might be submerged completelyin a suitable liquid, to clean the holder and/or to keep the holderuncontaminated. Besides, the computer control CC and/or the software maydetermine which of said various substrate holders is most likely to becontaminated and is to be rinsed or cleaned, or submerged, first.

In an alternative method, as has been described above and has beendepicted in FIG. 4, a respective immersion space at least extendsbetween a patterning device, a dummy patterning device or a patterningdevice shaped object MA and/or patterning device holder MT on one sideand a projection system PS on an opposite side. For example, a dummypatterning device or a patterning device shaped object MA can be placedon the patterning device holder MT, whereafter the respective immersionspace 10′ is being rinsed, for example during idle mode of theapparatus. Preferably, the apparatus includes an in-situ storage spaceor compartment (not shown) to store such a dummy patterning device or apatterning device shaped object MA, when that patterning device orobject is not being located on the patterning device holder. After therinsing, the dummy patterning device or the patterning device shapedobject can be replaced by a true patterning device, which is to be usedto pattern radiation before the radiation enters the projection systemPS. For example, the immersion system can wash or rinse at least part ofthe patterning device holder. Also, the immersion system can wash orrinse at least one slit or aperture E′ extending in or near thepatterning device holder WT (see FIG. 4). In case the apparatus includesat least two patterning device holders, the various patterning deviceholders can be treated similarly to the above-described method forpreventing or reducing contamination with respect to multiple substrateholders WT.

In case the apparatus 1 includes at least two patterning device supportsMT, the supports MT might be moved subsequently to respective firstposition, to be cleaned by the respective immersion system, similar tothe above described treatment of at least two substrate holders WT.Also, one or more of those patterning device supports MT might becleaned by an optional cleaning device (not shown), when those supportsMT are in respective second positions. Besides, the computer control CCand/or the software may determine which of said various patterningdevice supports MT is most likely to be contaminated and is to be rinsedor cleaned first.

The invention can be aimed at reducing contamination during start-up ofthe lithographic apparatus and/or reducing contamination on the firstsubstrate(s) of a batch of substrates. For example, the first substratesbeing processed by the apparatus after a machine idle time may show acontamination peak, for example in the number of particles. Said numbercan be expressed as the “Particle per Wafer Pass” (PWP) number. Besides,the invention can achieve a reduction of potential bacteria growth. Forexample, said rinsing can provide a continuous flow of fluid over arespective apparatus part (for example a substrate holder), which canprevent bacteria growth. Besides, by applying the optional in-situUV-light cleaning procedure, the utilization of a H₂O₂ cleaning methodto remove bacteria can be avoided. The use of H₂O₂ is not compatiblewith TiN, which might be present in certain components of the apparatus.

Usually, in a device manufacturing method, resist coated wafers are tobe illuminated by the apparatus. The use of resist coated wafers mayincrease the contamination level PWP, depending for example on theresist and the way it is applied to the substrate. This has beendepicted in FIG. 5. FIG. 5 shows results of different experimental testruns concerning the substrate stage of the immersion type apparatus.First, a PWP value was being determined using a bare silicon wafer,which had been loaded and unloaded to and from the substrate holder WTof the apparatus. The respective value was relatively low, and has beenplotted by a circle AA in FIG. 5.

Shortly after that, a batch of resist coated wafers (zero dose) wasexposed by the apparatus. Next, the PWP was again tested, using afurther 8 bare Si wafers. The respective 8 results, depicted in FIG. 5by diamonds BB, show an increase of the PWP.

Then, the rinsing of the immersion space was started, utilizing theimmersion system and immersion liquid, during a subsequent idle periodof the apparatus of about 9½ hrs. After that, a further 5 bare waferswere used to test the PWP again. Their results, depicted by triangles CCin FIG. 5, shown that the rinsing of the immersion space 10 led to adesired low PWP

Particularly, the PWP of a first wafer to be exposed in an operationalperiod of the apparatus can typically be much higher than of anysubsequently exposed wafers. Following the present invention, prolongedor substantially continuous wet hovering by the immersion system overthe substrate holder WT and/or patterning device holder MT, and/or partsthereof such as said edge seal member 17, slits E, E′, sensors and othercomponents, has been demonstrated to reduce the PWP.

In an embodiment, the apparatus can be configured to load bare siliconwafers on the substrate holder or substrate holders (or chucks of partsthereof), and to start wet hovering over the substrate holder(s). Forexample, such a rinsing can be carried out with a minimal number ofClosing Disk Exchanges, in case the apparatus has been provided with aso called closing disk or suitable closing member to close fluidsupplies 13 of said immersion system. The rinsing procedure can bestarted automatically after a given time of “machine idle” (compare witha “screen-saver”), and/or after a certain number of exposures. Forexample, a number of virgin wafers stored in a “pizza box shapedcontainer” in the Wafer Handler H, or in a different location, can beused for such cleaning actions.

When the apparatus includes two or more substrate holders or chucks,each of the substrate holders or chucks may be cleaned by swapping thesubstrate holders or chucks after a certain time frame. In addition,said computer control CC and/or said software might keep track of thesubstrate holder or chuck which was cleaned last, and start with theother one next time.

Also, to prevent bacteria growth on or near the substrate holder or thechuck, preferably during idle time of the apparatus, the substrateholder or chuck can be flushed continuously with the immersion liquid,for example with ultra pure water (UPW). Preferably, puddles ofnot-moving water which are exposed to air are avoided. In addition, saidradiation source SO might be switched on for a certain period of timeduring the flushing with the water, which can provide a UV-light inducedozone cleaning of the substrate holder or chuck. Such an ozone cleaningcan be effective for chemical contamination with an organic nature suchas spilled resist and to “kill” bacteria. During such a cleaningprocedure, preferably, a bare substrate or substrate shaped object ispresent on the substrate holder under treatment.

For example, during idle time of the apparatus, each substrate holder orchuck can be continuously flushed with UPW water to decrease particlecontamination and to avoid bacteria growth. Preferably, the immersionliquid is running at all times.

Also, during idle time, the radiation source SO light might be used toperform an in-situ cleaning, particularly when the source is an UV-lightradiation source. Ozone generated in the water is an effective means toremove organic and bacteria growth.

Also, bare dummy substrates, or objects with similar geometry to a barewafer, can be placed on the substrate holder WT during said idle timecleaning procedure. The immersion type apparatus can be equipped with adedicated in-situ storage compartment 22 for the dummy substrates.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” as used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the present invention may be applied to anyimmersion lithographic apparatus, such as those types mentioned above,and whether the immersion liquid is provided in the form of a bath oronly on a localized surface area of the substrate. An immersion systemcan be any mechanism that provides a liquid to a space between theprojection system and the substrate and/or substrate table. It maycomprise any combination of one or more structures, one or more liquidinlets, one or more gas inlets, one or more gas outlets, and/or one ormore liquid outlets, the combination providing and confining theimmersion liquid to the space. In an embodiment, a surface of the spacemay be limited to a portion of the substrate and/or substrate table, asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table.

Also, an immersion system can be any mechanism that provides a liquid toa space between the projection system and the patterning device and/orpatterning device support.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A method for preventing or reducing contamination of an immersiontype projection apparatus, the apparatus comprising at least oneimmersion space that is at least partially filled with a liquid when theapparatus projects a beam of radiation onto a substrate, the methodcomprising: rinsing at least part of the immersion space with a rinsingliquid before the apparatus is used to project the beam of radiationonto a substrate.
 2. A method according to claim 1, wherein the rinsingof the immersion space occurs during an idle operational mode of theapparatus.
 3. A method according to claim 1, wherein said liquid andsaid rinsing liquid are the same liquid.
 4. A method according to claim1, wherein the rinsing of the immersion space occurs substantiallycontinuously until the apparatus is used to project radiation onto asubstrate.
 5. A method according to claim 1, further comprisingilluminating at least part of the immersion space and/or the rinsingliquid with ultraviolet radiation.
 6. A method according to claim 1,wherein said immersion space at least extends between at least part of asubstrate, a dummy substrate or a substrate-shaped object and/or asubstrate holder on one side, and a projection system on an oppositeside.
 7. A method according to claim 6, further comprising: placing thedummy substrate or the substrate-shaped object on said substrate holder;and replacing the dummy substrate or the substrate-shaped object asubstrate to be illuminated by the projection system after the rinsinghas been completed.
 8. A method according to claim 1, wherein saidimmersion space at least extends between a patterning device, a dummypatterning device or a patterning device-shaped object and/or apatterning device holder on one side, and a projection system onopposite side.
 9. A method according to claim 8, further comprising:placing the dummy patterning device or the patterning device-shapedobject on said patterning device holder; and replacing the dummypatterning device or the patterning device-shaped object with apatterning device to be used to pattern radiation before the radiationenters the projection system.
 10. A method according to claim 1, whereinthe apparatus is a lithographic projection apparatus.
 11. A methodaccording to claim 1, further comprising: varying the location of theimmersion space during the rinsing of the immersion space to cleandifferent parts and/or areas of the apparatus.
 12. A method forpreventing or reducing contamination of a lithographic projectionapparatus, the apparatus including a substrate holder constructed tohold a substrate, a patterning device holder constructed to hold apatterning device, a projection system, and an immersion systemconfigured to at least partially fill an immersion space of theapparatus with a liquid, the method comprising: moving at least one ofthe immersion system and at least part of the apparatus relative to eachother; and rinsing said at least part of the apparatus with the liquidbefore the apparatus is used to project a patterned beam of radiationonto a target portion of a substrate.
 13. A method according to claim12, wherein said at least part of the apparatus comprises at least partof the substrate holder.
 14. A method according to claim 12, whereinsaid at least part of the apparatus comprises at least one slit oraperture extending in or near the substrate holder.
 15. A methodaccording to claim 12, wherein said at least part of the apparatuscomprises at least part of the patterning device holder.
 16. A methodaccording to claim 12, wherein said at least part of the apparatuscomprises at least one slit or aperture extending in or near thepatterning device holder.
 17. A method for preventing or reducingcontamination of a lithographic projection apparatus, the apparatusincluding an immersion space, the method comprising: filling at leastpart of the immersion space with a rinsing liquid for at least oneminute.
 18. A method according to claim 17, wherein the filling occurssubstantially continuously for at least one day, including at least oneidle operational period of the apparatus or a part thereof.
 19. A methodfor preventing or reducing contamination of a lithographic projectionapparatus, the apparatus including a substrate holder constructed tohold a substrate, a patterning device holder constructed to hold apatterning device, a projection system, and an immersion space, themethod comprising: filling at least part of the immersion space with arinsing liquid during an idle time of the apparatus to prevent or reducesubstrate contamination during at least one subsequent start-up run ofthe apparatus.
 20. A method according to claim 19, wherein the rinsingliquid consists of ultra pure water.
 21. An immersion type lithographicapparatus comprising: at least one immersion space; and an immersionsystem configured to at least partially fill the immersion space with aliquid, wherein the apparatus is configured to rinse at least part ofthe immersion space with a rinsing liquid before the apparatus is usedto project a patterned beam of radiation onto a substrate.
 22. Anapparatus according to claim 21, wherein the apparatus is configured torinse at least part of the immersion space during an idle operationalmode of the apparatus.
 23. An apparatus according to claim 21, whereinthe apparatus is configured to provide an object in said immersion spaceand/or in an adjoining position with respect to the immersion spaceduring the rinsing of that space, and to remove said object before theapparatus is used to project a radiation beam onto a target portion of asubstrate.
 24. An apparatus according to claim 23, further comprising atleast one storage space or compartment to store said object when theapparatus is used to project a radiation beam onto a target portion ofthe substrate.
 25. An apparatus according to claim 21, wherein theapparatus is configured to rinse the immersion space with said liquid.26. An apparatus according to claim 21, wherein the apparatus isconfigured to rinse the immersion space substantially continuously untilthe apparatus projects a radiation beam onto a substrate.
 27. Anapparatus according to claim 21, further comprising at least one ultraviolet radiation source configured to illuminate the immersion spacewith ultraviolet radiation during the rinsing of that space, before theapparatus is used to project a radiation beam onto a target portion of asubstrate.
 28. An apparatus according to claim 21, wherein saidimmersion space extends between at least part of a substrate, a dummysubstrate, a substrate-shaped object and/or a substrate holder on oneside and part of a projection system of the apparatus on an oppositeside.
 29. An apparatus according to claim 28, wherein the apparatus isconfigured to place the dummy substrate or the substrate-shaped objecton said substrate holder, and to subsequently rinse the respectiveimmersion space.
 30. An apparatus according to claim 28, wherein saidapparatus is configured to have the immersion space at least reach orinclude an outer contour of the substrate, the dummy substrate or thesubstrate-shaped object, being held by said substrate holder, during therinsing.
 31. An apparatus according to claim 21, wherein the apparatusis configured to rinse at least an area extending along an edge of asubstrate, a dummy substrate or a substrate-shaped object, being held bya substrate holder, using said immersion space and said rinsing liquid.32. An apparatus according to claim 21, wherein the apparatus isconfigured to rinse at least part of a surface of the substrate holderand/or one or more components that are located on that surface usingsaid immersion space and said rinsing liquid.
 33. An apparatus accordingto claim 32, wherein said components are selected from the groupconsisting of an edge seal member, a sensor, a positioning device, and amirror element.
 34. An apparatus according to claim 21, furthercomprising at least two substrate holders, wherein said immersion spaceextends between at least part of at least one of the substrate holderson one side and a projection system on an opposite side, and wherein theapparatus is configured to move each substrate holder to a firstposition and to a respective second position, away from said projectionsystem.
 35. An apparatus according to claim 34, wherein the apparatus isconfigured to subsequently move said substrate holders to said firstposition, to be at least partially rinsed in or near that position bysaid rinsing liquid.
 36. An apparatus according to claim 34, furthercomprising at least one cleaning device configured to at least partiallyclean at least one of the substrate holders when that substrate holderis in said second position.
 37. An apparatus according to claim 34,wherein the apparatus is configured to determine which of said substrateholders is most likely to be contaminated and to rinse or clean thesubstrate holder that has been found to be most likely contaminated,first.
 38. An apparatus according to claim 21, wherein said immersionspace at least extends between a patterning device and/or patterningdevice holder on one side and a projection system on an opposite side.39. An apparatus according to claim 38, wherein the apparatus isconfigured to place a dummy patterning device or a patterningdevice-shaped object on said patterning device holder, and tosubsequently rinse the immersion space.
 40. An apparatus according toclaim 28, wherein the apparatus is configured to move said substrateholder with respect to said projection system during the rinsing, suchthat the position of the immersion space changes with respect to thesubstrate holder during the rinsing.
 41. An apparatus according to claim21, wherein the apparatus is configured to start said rinsingautomatically after a predetermined amount of idle time of theapparatus.
 42. An apparatus according to claim 21, wherein the apparatusis configured to start said rinsing automatically after a predeterminednumber of substrate exposures.
 43. An apparatus according to claim 21,wherein the apparatus is configured to determine or estimate whether atleast part of said apparatus has reached a certain threshold amount ofcontamination, and to rinse said apparatus part when it has beendetermined or estimated that said apparatus part has reached thethreshold amount of contamination.
 44. An apparatus according to claim21, further comprising a computer control to control said rinsing. 45.An immersion type lithographic apparatus, including at least one storagespace or compartment to store at least one dummy substrate orsubstrate-shaped object in-situ.
 46. An immersion type lithographicapparatus, including at least one storage space or compartment to storeat least one dummy patterning device or patterning device-shaped objectin-situ.
 47. A computer program containing one or more sequences ofmachine-readable instructions configured to carry out a method forpreventing or reducing contamination of an immersion type projectionapparatus when the computer program is being executed by a computer, theapparatus comprising at least one immersion space that is at leastpartially filled with a liquid when the apparatus projects a beam ofradiation onto a substrate, the method comprising rinsing at least partof the immersion space with a rinsing liquid before the apparatus isused to project the beam of radiation onto a substrate.
 48. A method forpreventing or reducing contamination of a lithographic projectionapparatus comprising a space that is to be provided with a liquidthrough which a beam of radiation can be transmitted, the methodcomprising: operating the lithographic apparatus; and subsequentlyrinsing at least part of the space with a rinsing liquid.
 49. A methodaccording to claim 48, wherein said liquid and said rinsing liquid arethe same liquid.